One-time programmable memory bit cell

ABSTRACT

A memory bit cell includes a first memory cell including a first antifuse transistor and a first selection transistor, the first antifuse transistor being selectable between a first state or a second state in response to a word line program signal, the first selection transistor being configured to provide access to the first antifuse transistor in response to a word line read signal; a second memory cell including a second antifuse transistor and a second selection transistor, the second antifuse transistor being selectable between the first state or the second state in response to the word line program signal, the second selection transistor being configured to provide access to the second antifuse transistor in response to the word line read signal; a first word line to selectively provide the word line program signal; a second word line to selectively provide the word line read signal; and a bit line.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 17/233,771, filed Apr. 19, 2021, which is a continuation of application Ser. No. 16/787,312, filed Feb. 11, 2020, now U.S. Pat. No. 10,984,878, which applications are incorporated herein by reference in their entirety.

BACKGROUND

Many modern day electronic devices include electronic memory. Electronic memory is a device configured to store bits of data in respective memory cells. A memory cell is a circuit configured to store a bit of data, typically using one or more transistors. One type of an electronic memory is one-time programmable (OTP) memory. An OTP memory is a read-only memory that may be programmed (e.g., written to) only once.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a block diagram of a memory device in which aspects of the disclosure may be practiced in accordance with some embodiments.

FIG. 2 is a schematic diagram of an OTP memory cell in accordance with some embodiments.

FIG. 3 is a structure diagram of a memory array in accordance with some embodiments.

FIG. 4 is a layout diagram of the memory array of FIG. 3.

FIG. 5 is a structure diagram of a memory array in accordance with some embodiments.

FIG. 6 is a layout diagram of the memory array of FIG. 5.

FIG. 7 is an equivalent circuit diagram of four OTP memory cells of the memory array of FIG. 5.

FIG. 8 is a schematic diagram of eight OTP memory cells of the memory array of FIG. 5.

FIG. 9 is a flow chart illustrating a method for operating a memory device in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

One-time programmable (OTP) memory devices include electrical fuse (eFuse) and antifuse. An eFuse is programmed by electrically blowing a strip of metal or poly with a flow of high-density current using I/O voltage. An antifuse is programmed by electrically shorting the gate and source of a transistor with an dielectric breakdown when a high voltage is applied to the thin gate dielectric layer of the transistor. Examples of the gate dielectric materials may include high-k dielectric, silicon dioxide, and silicon oxynitride, though other gate dielectric materials may also be employed. The thickness of the thin gate dielectric layer is lower than the thickness of a regular gate dielectric layer. An antifuse starts with a high resistance state and ends up with a permanent electrically conductive path (a low resistance state).

Typically, an OTP memory device using antifuse has a two-transistor (2T) per bit arrangement. Specifically, each bit corresponds to a cell. Each cell has a two-transistor structure including two transistors: an antifuse transistor and a selection transistor. However, the cell with the two-transistor structure may have a small cell current which is hard to be read on-cell. Moreover, in order to reduce path resistance, it is difficult to put vertical interconnect accesses (vias) on active regions (OD regions) and gate (poly) strips to connect metal tracks for bit line (BL) signals and word line (WL) signals.

In accordance with some disclosed examples, multiple (e.g., two or four) OTP memory cells are used to form a bit cell which stores one bit of data. The multiple OTP memory cells in the same bit cell share a first word line, a second word line, and a bit line. Compared with the two-transistor per bit (i.e., 1 cell per bit) arrangement, the multiple cells per bit arrangement results in a bigger current which is easier to be read on-cell. The flexibility to put vias on active regions and gate strips to connect metal tracks for bit line signals and word line signals increases.

FIG. 1 illustrates a block diagram of a memory device 100 in which aspects of the disclosure may be practiced in accordance with some embodiments. In the illustrated embodiment, the memory device 100 includes memory cells 102 that are arranged in rows and columns to form a memory array 104. The memory device 100 can include any suitable number of rows and columns. For example, a memory device includes R number of rows and C number of columns, where R is an integer greater than or equal to 1 and C is a number greater than or equal to 2. As will be described in more detail later, in one embodiment the memory cells 102 are OTP memory cells that include an antifuse transistor and a selection transistor.

Each row of memory cells 102 is operatively connected to one or more word lines (collectively word line 106). The word lines 106 are operatively connected to one or more row select circuits (collectively referred to as row select circuit 108). The row select circuit 108 selects a particular word line 106 based on an address signal that is received on a signal line 110.

Each column of memory cells 102 is operatively connected to one or more bit lines (collectively bit line 112). The bit lines 112 are operatively connected to one or more column select circuits (collectively referred to as column select circuit 114). The column select circuit 114 selects a particular bit line 112 based on a select signal that is received on a signal line 116. It should be noted that the arrangement of rows and columns can be different from the illustrated example in FIG. 1 in other embodiments. In other words, each row of memory cells 102 may be operatively connected to one or more bit lines 112, whereas each column of memory cells 102 may be operatively connected to one or more word lines 106.

A processing device 118 is operatively connected to the memory array 104, the row select circuit 108, and the column select circuit 114. The processing device 118 is operable to control one or more operations of the memory array 104, the row select circuit 108, and the column select circuit 114. Any suitable processing device can be used. Example processing devices include, but are not limited to, a central processing unit, a microprocessor, an application specific integrated circuit, a graphics processing unit, a field programmable gate array, or combinations thereof.

A power supply 120 is at least operatively connected to the memory array 104 and the processing device 118. The processing device 118 can cause one or more bias voltages to be applied to the memory cells 102 in the memory array 104.

The processing device 118 and/or the power supply 120 can be disposed in the same circuitry (e.g., the same integrated circuit) as the memory array 104, or the processing device 118 and/or the power supply 120 may be disposed in separate circuitry from the memory array 104 and operatively connected to the memory array 104. The memory device 100, the processing device 118, and the power supply 120 are included in an electronic device 122. Example electronic devices include, but are not limited to, a computing device, a television, a camera, and a wearable device.

When data is to be written to a memory cell 102 (e.g., the memory cell 102 is programmed), or read from a memory cell 102, an address for the memory cell is received on signal line 110. The row select circuit 108 activates or asserts the word line 106 associated with the address. A select signal is received on the signal line 116 and the bit line 112 associated with the select signal is asserted or activated. The data is then written to, or read from, the memory cell 102.

FIG. 2 depicts a schematic diagram of an OTP memory cell in accordance with some embodiments. The OTP memory cell 102 is formed with a first transistor 202 connected in series with a second transistor 204. In the illustrated example, the first transistor 202 is an antifuse transistor 202, and the second transistor 204 is a selection transistor 204. The thickness of a gate dielectric layer of the antifuse transistor 202 is lower than the thickness of a gate dielectric layer of the selection transistor 204. A gate of the antifuse transistor 202 receives a word line program (WLP) signal on a word line 106P. A gate of the selection transistor 204 receives a word line read (WLR) signal on another word line 106R. A source or a drain of the selection transistor 204 is connected to a bit line 112. Any suitable type of transistor can be used. In one embodiment, the antifuse transistor 202 and the selection transistor 204 are metal oxide semiconductor (MOS) transistors. In another embodiments, the antifuse transistor 202 and the selection transistor 204 are fin field-effect transistors (FinFETs). In one embodiment, the antifuse transistor 202 may be n-type as illustrated in FIG. 2. In another embodiment, the antifuse transistor 202 may be p-type. In one embodiment, the selection transistor 204 may be n-type as illustrated in FIG. 2. In another embodiment, the selection transistor 204 may be p-type.

During programming, a high voltage is applied to a thin gate dielectric layer of the antifuse transistor 202. As a result, a resultant avalanche breakdown causes the gate and source of the antifuse transistor 202 to be shorted. Thus, the antifuse transistor 202 is in a low resistance state with a permanent electrically conductive path. In the illustrated example, the selection transistor 204 is an n-type transistor. When the WLR signal is at logical high (i.e., “1”), the selection transistor 204 is turned on. When the bit line 112 is asserted or activated, data is then written to, or read from, the memory cell 102. In summary, the antifuse transistor 202 is configured to store a first state (e.g., a low resistance state) or a second state (e.g., a high resistance state) in response to the WLP signal provided on a first word line 106P, the selection transistor 204 is configured to provide access to the antifuse transistor 202 in response to a WLR signal provided on a second word line 106R, and the selection transistor 204 is electrically connected to a bit line 112 for sensing the first state or the second state. As such, a bit of data corresponding to the first state or the second state is written to, or read from, the memory cell 102.

FIG. 3 is a structure diagram of a memory array in accordance with some embodiments. FIG. 4 is a layout diagram of the memory array of FIG. 3. FIG. 3 is described in conjunction with FIG. 4. In the illustrated example, a memory array 104 includes 16 OTP memory cells 102 a-102 p (collectively 102). The 16 OTP memory cells 102 a-102 p are arranged in 8 rows and 2 columns. Each of the 16 OTP memory cells 102 a-102 p has a two-transistor structure as shown in FIG. 2.

In the first column, gates of antifuse transistors of the OTP memory cells 102 a, 102 b, 102 e, 102 f, 102 i, 102 j, 102 m, and 102 n are connected to a word line 106P that receives a WLP signal WLP0, while gates of selection transistors of the OTP memory cells 102 a, 102 b, 102 e, 102 f, 102 i, 102 j, 102 m, and 102 n are connected to a word line 106R that receives a WLR signal WLR0. In the second column, gates of antifuse transistors of the OTP memory cells 102 c, 102 d, 102 g, 102 h, 102 k, 102 l, 102 o, and 102 p are connected to another word line 106P that receives another WLP signal WLP1, while gates of selection transistors of the OTP memory cells 102 c, 102 d, 102 g, 102 h, 102 k, 102 l, 102 o, and 102 p are connected to a word line 106R that receives another WLR signal WLR1.

In a first row, the OTP memory cells 102 a and 102 c are connected in series. In a second row, the OTP memory cells 102 b and 102 d are connected in series. In a third row, the OTP memory cells 102 e and 102 g are connected in series. In a fourth row, the OTP memory cells 102 f and 102 h are connected in series. In a fifth row, the OTP memory cells 102 i and 102 k are connected in series. In a sixth row, the OTP memory cells 102 j and 102 l are connected in series. In a seventh row, the OTP memory cells 102 m and 102 o are connected in series. In an eighth row, the OTP memory cells 102 n and 102 p are connected in series.

The OTP memory cells 102 a, 102 b, 102 c, and 102 d are all connected to a bit line 112 that receives a signal BL0. As such, the OTP memory cells 102 a and 102 b together are used to store 1 bit of data. In other words, two OTP memory cells are used per bit. A bit cell 302 includes two OTP memory cells: the OTP memory cells 102 a and 102 b. Only one bit cell 302 is identified in FIG. 3 for simplicity. Likewise, the OTP memory cells 102 c and 102 d together are used to store 1 bit of data. The OTP memory cells 102 e, 102 f, 102 g, and 102 h are all connected to a bit line 112 that receives a signal BL1. As such, the OTP memory cells 102 e and 102 f together are used to store 1 bit of data, whereas the OTP memory cells 102 g and 102 h together are used to store 1 bit of data. The OTP memory cells 102 i, 102 j, 102 k, and 102 l are all connected to a bit line 112 that receives a signal BL2. As such, the OTP memory cells 102 i and 102 j together are used to store 1 bit of data, whereas the OTP memory cells 102 k and 102 l together are used to store 1 bit of data. The OTP memory cells 102 m, 102 n, 102 o, and 102 p are all connected to a bit line 112 that receives a signal BL3. As such, the OTP memory cells 102 m and 102 n together are used to store 1 bit of data, whereas the OTP memory cells 102 o and 102 p together are used to store 1 bit of data. In summary, the memory array 104 includes 16 OTP memory cells 102 a-102 p and 8 bit cells 302 in the illustrated four-transistor per bit (i.e., 2 cells per bit) arrangement.

Now referring to FIG. 4, a layout of the memory array 104 of FIG. 3 is illustrated. Eight active regions (OD regions) 410 a-410 h (collectively 410) are disposed on a substrate and extend in an X direction.

Four gate (poly) strips 420 a, 420 b, 420 c, and 420 d are disposed on the eight active regions 410 a-410 h and extend in a Y direction. The Y direction is perpendicular to the X direction. The gate strip 420 a serves as gates of antifuse transistors and the WLP signal WLP0 on the word line 106P can be applied to the gate strip 420 a. The gate strip 420 b serves as gates of selection transistors and the WLR signal WLR0 on the word line 106R can be applied to the gate strip 420 b. The gate strip 420 c serves as gates of selection transistors and the WLR signal WLR1 on the word line 106R can be applied to the gate strip 420 c. The gate strip 420 d serves as gates of antifuse transistors and the WLP signal WLP1 on the word line 106P can be applied to the gate strip 420 d.

For simplicity, only the OTP memory cells 102 c and 102 d are described in detail. As mentioned earlier, the OTP memory cells 102 c and 102 d together are used to store 1 bit of data. The OTP memory cell 102 c includes a selection transistor 204 c and an antifuse transistor 202 c, both of which are located in the active region 410 a. The gate strip 420 c serves as a gate of the selection transistor 204 c whereas the gate strip 420 d serves as a gate of the antifuse transistor 202 c. The gate of the antifuse transistor 202 c is connected to a metal track 432 c through a vertical interconnect access (via) VG 450 c. The metal track 432 c can receive the WLP signal WLP1. A source or a drain of the selection transistor 204 c is connected to a metal track 434 a through a via VD 460 a. The metal track 434 a can receive the signal BL0.

Likewise, the OTP memory cell 102 d includes a selection transistor 204 d and an antifuse transistor 202 d, both of which are located in the active region 410 b. The gate strip 420 c serves as a gate of the selection transistor 204 d whereas the gate strip 420 d serves as a gate of the antifuse transistor 202 d. The gate of the antifuse transistor 202 d is connected to a metal track 432 d through a via VG 450 d. The metal track 432 d can receive the WLP signal WLP1. A source or a drain of the selection transistor 204 d is connected to the metal track 434 a through a via VD 460 b. The metal track 434 a can receive the signal BL0. As such, both the OTP memory cell 102 c and the OTP memory cell 102 d are connected to the metal track 434 a through the via VD 460 a and the via VD 460 b, respectively. Since the selection transistor 204 c and the selection transistor 204 d are both controlled by the WLR signal WLR1, the OTP memory cells 102 c and 102 d together are used to store 1 bit of data. In other words, two OTP memory cells are used per bit.

In terms of layout area, the width (e.g., two fin counts) of active regions 410 a-410 h of the four-transistor per bit (i.e., 2 cells per bit) arrangement is half of the width (e.g., four fin counts) of active regions of a two-transistor per bit (i.e., 1 cell per bit) arrangement, the overall layout areas are the same while cell current of the four-transistor per bit (i.e., 2 cells per bit) arrangement increases, which will be explained in detail later.

FIG. 5 is a structure diagram of a memory array in accordance with some embodiments. FIG. 6 is a layout diagram of the memory array of FIG. 5. FIG. 7 is an equivalent circuit diagram of four OTP memory cells of the memory array of FIG. 5. FIG. 8 is a schematic diagram of eight OTP memory cells of the memory array of FIG. 5. FIG. 5 is described in conjunction with FIGS. 6-8. In the illustrated example, a memory array 104 includes 16 OTP memory cells 102 a-102 p (collectively 102). The 16 OTP memory cells 102 a-102 p are arranged in 8 rows and 2 columns. Each of the 16 OTP memory cells 102 l-102 p has a two-transistor structure as shown in FIG. 2.

In the first column, gates of antifuse transistors of the OTP memory cells 102 a, 102 b, 102 e, 102 f, 102 i, 102 j, 102 m, and 102 n are connected to a word line 106P that receives a WLP signal WLP0, while gates of selection transistors of the OTP memory cells 102 a, 102 b, 102 e, 102 f, 102 i, 102 j, 102 m, and 102 n are connected to a word line 106R that receives a WLR signal WLR0. In the second column, gates of antifuse transistors of the OTP memory cells 102 c, 102 d, 102 g, 102 h, 102 k, 102 l, 102 o, and 102 p are connected to another word line 106P that receives another WLP signal WLP1, while gates of selection transistors of the OTP memory cells 102 c, 102 d, 102 g, 102 h, 102 k, 102 l, 102 o, and 102 p are connected to a word line 106R that receives another WLR signal WLR1.

In a first row, the OTP memory cells 102 a and 102 c are connected in series. In a second row, the OTP memory cells 102 b and 102 d are connected in series. In a third row, the OTP memory cells 102 e and 102 g are connected in series. In a fourth row, the OTP memory cells 102 f and 102 h are connected in series. In a fifth row, the OTP memory cells 102 i and 102 k are connected in series. In a sixth row, the OTP memory cells 102 j and 102 l are connected in series. In a seventh row, the OTP memory cells 102 m and 102 o are connected in series. In an eighth row, the OTP memory cells 102 n and 102 p are connected in series.

The OTP memory cells 102 a, 102 b, 102 c, 102 d, 102 e, 102 f, 102 g, and 102 h are all connected to a bit line 112 that receives a signal BL0. As such, the OTP memory cells 102 a, 102 b, 102 e, and 102 f together are used to store 1 bit of data. In other words, four OTP memory cells are used per bit. A bit cell 502 includes four OTP memory cells: the OTP memory cells 102 a, 102 b, 102 e, and 102 f. Only one bit cell 502 is identified in FIG. 5 for simplicity. Likewise, the OTP memory cells 102 c, 102 d, 102 g, and 102 h together are used to store 1 bit of data. The OTP memory cells 102 i, 102 j, 102 k, 102 l, 102 m, 102 n, 102 o, and 102 p are all connected to a bit line 112 that receives a signal BL1. As such, the OTP memory cells 102 i, 102 j, 102 m, and 102 n together are used to store 1 bit of data, whereas the OTP memory cells 102 k, 102 l, 102 o, and 102 p together are used to store 1 bit of data. In summary, the memory array 104 includes 16 OTP memory cells 102 a-102 p and 4 bit cells 502 in the illustrated eight-transistor per bit (i.e., 4 cells per bit) arrangement.

Now referring to FIG. 6, a layout of the memory array 104 of FIG. 5 is illustrated. Eight active regions (OD regions) 410 a-410 h (collectively 410) are disposed on a substrate and extend in an X direction.

Four gate (poly) strips 420 a, 420 b, 420 c, and 420 d are disposed on the eight active regions 410 a-410 h and extend in a Y direction. The Y direction is perpendicular to the X direction. The gate strip 420 a serves as gates of antifuse transistors and the WLP signal WLP0 on the word line 106P can be applied to the gate strip 420 a. The gate strip 420 b serves as gates of selection transistors and the WLR signal WLR0 on the word line 106P can be applied to the gate strip 420 b. The gate strip 420 c serves as gates of selection transistors and the WLR signal WLR1 on the word line 106P can be applied to the gate strip 420 c. The gate strip 420 d serves as gates of antifuse transistors and the WLP signal WLP1 on the word line 106P can be applied to the gate strip 420 d.

For simplicity, only the OTP memory cells 102 c, 102 d, 102 g, and 102 h are described in detail. As mentioned earlier, the OTP memory cells 102 c, 102 d, 102 g, and 102 h together are used to store 1 bit of data. The OTP memory cell 102 c includes a selection transistor 204 c and an antifuse transistor 202 c, both of which are located in the active region 410 a. The gate strip 420 c serves as a gate of the selection transistor 204 c whereas the gate strip 420 d serves as a gate of the antifuse transistor 202 c. The gate of the antifuse transistor 202 c is connected to a metal track 432 c through a via VG 450 c. The metal track 432 c can receive the WLP signal WLP1. A source or a drain of the selection transistor 204 c is connected to a metal track 434 a through a via VD 460 a. The metal track 434 a can receive the signal BL0.

Likewise, the OTP memory cell 102 d includes a selection transistor 204 d and an antifuse transistor 202 d, both of which are located in the active region 410 b. The gate strip 420 c serves as a gate of the selection transistor 204 d whereas the gate strip 420 d serves as a gate of the antifuse transistor 202 d. The gate of the antifuse transistor 202 d is connected to a metal track 432 d through a via VG 450 d. The metal track 432 d can receive the WLP signal WLP1. A source or a drain of the selection transistor 204 d is connected to the metal track 434 a through a via VD 460 b. The metal track 434 a can receive the signal BL0.

Likewise, the OTP memory cell 102 g includes a selection transistor 204 g and an antifuse transistor 202 g, both of which are located in the active region 410 c. The gate strip 420 c serves as a gate of the selection transistor 204 g whereas the gate strip 420 d serves as a gate of the antifuse transistor 202 g. The gate of the antifuse transistor 202 g is connected to a metal track 432 g through a via VG 450 g. The metal track 432 g can receive the WLP signal WLP1. A source or a drain of the selection transistor 204 g is connected to the metal track 434 a through a via VD 460 c. The metal track 434 a can receive the signal BL0.

Likewise, the OTP memory cell 102 h includes a selection transistor 204 h and an antifuse transistor 202 h, both of which are located in the active region 410 d. The gate strip 420 c serves as a gate of the selection transistor 204 h whereas the gate strip 420 d serves as a gate of the antifuse transistor 202 h. The gate of the antifuse transistor 202 h is connected to a metal track 432 h through a via VG 450 h. The metal track 432 h can receive the WLP signal WLP1. A source or a drain of the selection transistor 204 h is connected to the metal track 434 a through a via VD 460 d. The metal track 434 a can receive the signal BL0. As such, the OTP memory cells 102 c, 102 d, 102 g, and 102 h are connected to the metal track 434 a through the via VD 460 a, the via VD 460 b, the via VD 460 c, and the via VD 460 d, respectively. Since the selection transistors 204 c, 204 d, 204 g, and 204 h are all controlled by the WLR signal WLR1, the OTP memory cells 102 c, 102 d, 102 g, and 102 h together are used to store 1 bit of data. In other words, four OTP memory cells are used per bit.

In terms of layout area, the width (e.g., two fin counts) of active regions 410 a-410 h of the eight-transistor per bit (i.e., 4 cells per bit) arrangement is half of the width (e.g., four fin counts) of active regions of a two-transistor per bit (i.e., 1 cell per bit) arrangement, the overall layout areas are the same while cell current of the eight-transistor per bit (i.e., 4 cells per bit) arrangement increases, which will be explained in detail with reference of FIG. 7.

Now referring to FIG. 7, an equivalent circuit including the OTP memory cells 102 c, 102 d, 102 g, and 102 h are illustrated. As mentioned earlier, the OTP memory cells 102 c, 102 d, 102 g, and 102 h are used to store 1 bit of data. By applying an appropriate voltage for the WLP signal WLP1, the antifuse transistors 202 c, 202 d, 202 g, and 202 h are in a low resistance state. As such, each of the antifuse transistors 202 c, 202 d, 202 g, and 202 h functions as a resistor with a resistance of R_(cell). By applying an appropriate voltage for the WLR signal WLR1, the selection transistors 204 c, 204 d, 204 g, and 204 h are turned on. Accordingly, each of the OTP memory cells 102 c, 102 d, 102 g, and 102 h has a current I_(read) flowing to the bit line 112. As a result, the current on the bit line 112 is 4I_(read) since four OTP memory cells 102 c, 102 d, 102 g, and 102 h are connected in parallel. Compared with the two-transistor per bit (i.e., 1 cell per bit) arrangement, the eight-transistor per bit (i.e., 4 cells per bit) arrangement illustrated in FIGS. 5-8 results in a bigger current which is easier to be read on-cell. It should be noted that the four-transistor per bit (i.e., 2 cells per bit) arrangement illustrated in FIGS. 3-4 also results in a bigger current compared with the two-transistor per bit (i.e., 1 cell per bit) arrangement.

Now referring to FIG. 8, the eight-transistor per bit (i.e., 4 cells per bit) arrangement illustrated. Specifically, the OTP memory cells 102 c, 102 d, 102 g, and 102 h are used to store 1 bit of data. Likewise, the OTP memory cells 102 a, 102 b, 102 e, and 102 f are used to store 1 bit of data. From a transistor perspective, the OTP memory cells 102 c, 102 d, 102 g, and 102 h have eight transistors. In this illustrated example, there are four antifuse transistors 202 and four selection transistors 204. It should be noted that in other embodiments of the eight-transistor per bit (i.e., 4 cells per bit) arrangement, there may be n antifuse transistors 202 and m selection transistors 204, where n is an integer greater or equal to 1 and m is an integer greater or equal to 1. Further, m and n may be different.

FIG. 9 is a flow chart illustrating a method for operating a memory device, such as the example memory device 101 shown in FIG. 1, in accordance with some embodiments. At step 902, a program signal is applied to a first word line electrically connected to a gate terminal of a first antifuse transistor and a gate terminal of a second antifuse transistor to select a first state or a second state of the first and second antifuse transistors. At step 904, a read signal is applied to a second word line electrically connected to a gate terminal of a first selection transistor and a gate terminal of a second selection transistor. The first and second selection transistors are connected in series to the first and second antifuse transistors, respectively. At step 906, the first or the second state of the first and second antifuse transistors on a bit line is sensed. The bit line is electrically connected to the first and second selection transistors.

In one aspect, a memory bit cell is provided. The memory bit cell includes a first memory cell including a first antifuse transistor and a first selection transistor electrically connected in series, the first antifuse transistor being selectable between a first state or a second state in response to a first signal, the first selection transistor being configured to provide access to the first antifuse transistor in response to a second signal; a second memory cell including a second antifuse transistor and a second selection transistor electrically connected in series, the second antifuse transistor being selectable between the first state or the second state in response to the first signal, the second selection transistor being configured to provide access to the second antifuse transistor in response to the second signal; a first word line connected to gate terminals of the first and second antifuse transistors to selectively provide the first signal to the first and second antifuse transistors; a second word line connected to gate terminals of the first and second selection transistors to selectively provide the second signal to the first and second selection transistors; and a bit line electrically connected to the first and second selection transistors for sensing the first state or the second state of the first and second antifuse transistors.

In another aspect, a memory device is provided. The memory device includes a memory array having an array of memory bit cells, the array having a plurality of columns and a plurality of rows, and each memory bit cell having: a first memory cell including a first antifuse transistor and a first selection transistor electrically connected in series, the first antifuse transistor being selectable between a first state or a second state in response to a first signal, the first selection transistor being configured to provide access to the first antifuse transistor in response to a second signal; a second memory cell including a second antifuse transistor and a second selection transistor electrically connected in series, the second antifuse transistor being selectable between the first state or the second state in response to the first signal, the second selection transistor being configured to provide access to the second antifuse transistor in response to the second signal; a first word line connected to gate terminals of the first and second antifuse transistors to selectively provide the first signal to the first and second antifuse transistors; a second word line connected to gate terminals of the first and second selection transistors to selectively provide the second signal to the first and second selection transistors; and a bit line electrically connected to the first and second selection transistors for sensing the first state or the second state of the first and second antifuse transistors. The memory device further includes a column select circuit for selecting a column of the plurality of columns; and a row select circuit for selecting a row of the plurality of rows.

In yet another aspect, a method is provided. The method includes applying a program signal to a first word line electrically connected to a gate terminal of a first antifuse transistor and a gate terminal of a second antifuse transistor to select a first state or a second state of the first and second antifuse transistors; applying a read signal to a second word line electrically connected to a gate terminal of a first selection transistor and a gate terminal of a second selection transistor, the first and second selection transistors connected in series to the first and second antifuse transistors, respectively; and sensing the first or the second state of the first and second antifuse transistors on a bit line electrically connected to the first and second selection transistors.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A memory bit cell, comprising: a first memory cell including a first antifuse transistor and a first selection transistor electrically connected in series; a second memory cell including a second antifuse transistor and a second selection transistor electrically connected in series; a first word line configured to receive a program signal, the first word line connected to gate terminals of the first and second antifuse transistors; a second word line configured to receive a read signal, the second word line connected to gate terminals of the first and second selection transistors; and a bit line electrically connected to a source or drain terminal of the first and second selection transistors.
 2. The memory bit cell of claim 1, wherein the first antifuse transistor is selectable between a first state or a second state in response to the word line program signal, and wherein the second antifuse transistor is selectable between the first state or the second state in response to the word line program signal.
 3. The memory bit cell of claim 1, wherein the first selection transistor is configured to provide access to the first antifuse transistor in response to the word line read signal, and wherein the second selection transistor is configured to provide access to the second antifuse transistor in response to the word line read signal.
 4. The memory bit cell of claim 2, wherein the first state is a low resistance state and the second state is a high resistance state.
 5. The memory bit cell of claim 2, wherein each of the first and second antifuse transistors has a permanent electrically conductive path associated with the first state.
 6. The memory bit cell of claim 1, wherein a first thickness of gate dielectric layers of the first and second antifuse transistors is less than a second thickness of gate dielectric layers of the first and second selection transistors.
 7. The memory bit cell of claim 1, wherein the first and second antifuse transistors are n-type.
 8. The memory bit cell of claim 1, wherein the first and second antifuse transistors are p-type.
 9. The memory bit cell of claim 1, wherein the first antifuse transistor and the first selection transistor include a first active area on or over a substrate extending in a first direction, and wherein the second antifuse transistor and the second selection transistor include a second active area on or over the substrate extending in the first direction.
 10. The memory bit cell of claim 9, wherein the first word line includes a first conductive gate strip extending over the first active area and the second active area in a second direction crossing the first direction, the first conductive gate strip connected to gates of the first and second antifuse transistors, and wherein the second word line includes a second conductive gate strip extending over the first active area and the second active area in the second direction connected to gates of the first and second selection transistors;
 11. The memory bit cell of claim 10, further comprising a conductive track extending over the first active area and the second active area in the second direction connected to a drain or a source of the first selection transistor and to a drain or a source of the second selection transistor.
 12. A memory bit cell, comprising: a substrate; a first active area on or over the substrate extending in a first direction, the first active area including a first antifuse transistor and a first selection transistor; a second active area on or over the substrate extending in the first direction, the second active area including a second antifuse transistor and a second selection transistor; a first conductive gate strip extending over the first active area and the second active area in the second direction, the first conductive gate strip connected to gates of the first and second antifuse transistors; a second conductive gate strip extending over the first active area and the second active area in the second direction, the second conductive gate strip connected to gates of the first and second selection transistors; and a conductive track extending over the first active area and the second active area in the second direction, the conductive track connected to a drain or a source of the first selection transistor and to a drain or a source of the second selection transistor.
 13. The memory bit cell of claim 12, wherein the first conductive gate strip is configured to receive a word line program signal, and wherein the first antifuse transistor is selectable between a first state or a second state in response to the word line program signal, and the second antifuse transistor is selectable between the first state or the second state in response to the word line program signal.
 14. The memory bit cell of claim 13, wherein each of the first and second antifuse transistors has a permanent electrically conductive path associated with the first state.
 15. The memory bit cell of claim 12, the second conductive gate strip is configured to receive a word line read signal, and wherein the first selection transistor is configured to provide access to the first antifuse transistor in response to the word line read signal, and the second selection transistor is configured to provide access to the second antifuse transistor in response to the word line read signal.
 16. The memory device of claim 12, wherein a first thickness of gate dielectric layers of the first and second antifuse transistors is less than a second thickness of gate dielectric layers of the first and second selection transistors.
 17. The memory bit cell of claim 12, wherein the first and second antifuse transistors are n-type.
 18. The memory bit cell of claim 12, wherein the first and second antifuse transistors are p-type.
 19. A method, comprising: applying a program signal to a first word line electrically connected to gate terminals of a plurality of antifuse transistors to select a first state or a second state of the plurality of antifuse transistors; applying a read signal to a second word line electrically connected to gate terminals of a plurality of selection transistors, each of the plurality of selection transistors connected in series with a corresponding one of the plurality of antifuse transistors; and sensing a read signal on a bit line electrically connected to the plurality of selection transistors.
 20. The method of claim 19, wherein applying the program signal to the first word line includes creating a permanent electrically conductive path in the plurality of antifuse transistors associated with the first state. 